# Public Switched Telephone Network (PSTN)

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The Video SDK call out feature allows users to join Video SDK sessions completely over the phone or use their phone as the audio connection to the session while viewing the Video on Windows. This is useful when:

-   You do not have a microphone or speaker on your computer.
-   You do not have an iOS or Android smartphone.
-   You cannot connect to a network for a video session with computer audio (VoIP).

See [Customize audio conferencing](/docs/video-sdk/account/#customize-audio-conferencing) for details.

## Prerequisites

-   [Video SDK Account](https://zoom.us/pricing/developer)
-   [Audio Conferencing Plan](https://zoom.us/billing)

## Make a call

Use `video_sdk_obj->getPhoneHelper();` to make a call.

-   Provide the name if the user will join completely by phone.
-   If the user is already connected to the session, but wants to use their phone for the audio portion, the name will default to the name provided in the `session_context`.

```cpp
IZoomVideoSDKPhoneHelper* m_phonehelper= video_sdk_obj->getPhoneHelper();
if (m_phonehelper->isSupportPhoneFeature()){
    m_phonehelper->inviteByPhone(L"+1",L"2025550176",L"Alice");
}
```

## Get call status

Use `getInviteByPhoneStatus` to find out about the status of the call, for example, ringing, accepted, hangup, etc.

```cpp
IZoomVideoSDKPhoneHelper* m_phonehelper= video_sdk_obj->getPhoneHelper();
m_phonehelper.getInviteByPhoneStatus();
```

## Receive call status

You can receive the call status and failure reason under the `onInviteByPhoneStatus` callback under `IZoomVideoSDKDelegate`.

```cpp
virtual void onInviteByPhoneStatus(PhoneStatus status, PhoneFailedReason 	reason) {
	printf("Current invitation status: %s\n",status);
printf("Reason of failure: %s\n",reason);
};
```